举例说明自定义C++异常处理的实例分享

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举例说明自定义C++异常处理的实例

例1：自定义一个继承自excepton的异常类myException

C++标准中，定义在<stdexcept>中的任何异常类都派生自exception Class，本例也只是简单地由exception继承，在try段抛出一个异常并捕捉。代码如下：

  /*++ test.cpp   version:1.0   decript:define a exception class named myException       derived from base class exception       which is declared in <exception>   created:2011-08-14   author: btwsmile   --*/   #include<exception>   #include<iostream>   using namespace std;      //customized exception class 'myException'   class myException:public exception   {   public:     myException():exception("ERROR! Don't divide a number by integer zero.n")     {     }   };   //entry of the application   int main()   {     int x=100,y=0;     try     {       if(y==0) throw myException();       else cout<<x/y;     }     catch(myException& me)     {       cout<<me.what();     }     system("pause");     return 0;   }   

结果如下：

  ERROR! Don't divide a number by integer zero.  

请按任意键继续. . .                                                 

显然，异常被捕捉到了。此处需要说明的是，VC对异常处理类exception进行了扩展，本例之所以能够使用exception(“ERROR!….”)的初始化方法正出于这样的原因，C++标准是不允许这样做的。

与此同时，VC又没有遵循标准，有力地支持terminate和unexpected，它只保留了语法，却在编译运行时不提供支持。为了结合terminate和unexpected更加深入了解C++的异常处理，下面的例子采用Dev cpp IDE实现。

例2：依照C++标准实现自定义异常类myException并将throw语句封装到函数check()中涉及到的更改正如标题所述，（1）重写基类的what()函数，返回错误信息；（2）将throw myException()封装到check()函数中；(3)允许check()函数抛出myException类型的异常。代码如下：

  /*++ test.cpp   version:1.1   decript:define a exception class named myException       according to C++ standard,       derived from base class exception       which is declared in <exception>       !also,encapusulate throw into a function   created:2011-08-14   author: btwsmile   --*/   #include<exception>   #include<iostream>   using namespace std;      //customized exception class 'myException'   class myException:public exception   {   public:     const char* what()const throw()//#1      {       return "ERROR! Don't divide a number by integer zero.n";     }     };   void check(int y) throw(myException)//#2   {      if(y==0) throw myException();   }   //entry of the application   int main()   {     int x=100,y=0;     try     {       check(y);       cout<<x/y;     }     catch(myException& me)     {       cout<<me.what();     }     system("pause");     return 0;   }   

结果与例1完全相同。需说明的是，紧跟check()后的throw列表表明允许该函数抛出的异常类型。这里不得不产生疑问，如果抛出了一个不被允许的异常类型将怎样？

例3：抛出unexpected异常

check函数体之后的throw列表，规定了允许抛出的异常类型，一旦违背，就将触发unexpected。可以把unexpected看作系统自动调用的CALLBACK函数，不同的是，也可以手工触发它的执行。本例的情况属于前者。代码如下：

     /*++ test.cpp   version:1.3   decript:define an unexpected excption handler,       set it by using set_unexpected,       modify the throw list of function check   created:2011-08-14   author: btwsmile   --*/   #include<exception>   #include<iostream>   using namespace std;      //customized exception class 'myException'   class myException:public exception   {   public:     const char* what()const throw()     {       return "ERROR! Don't divide a number by integer zero.n";     }     };   void check(int y) throw()//#1 only int-type exception is permitted   {      if(y==0) throw myException();   }   void myUnexpected()   {      cout<<"Unexpected exception caught!n";      system("pause");      exit(-1);   }   //entry of the application   int main()   {     unexpected_handler oldHandler=set_unexpected(myUnexpected);     int x=100,y=0;     try     {       check(y);       cout<<x/y;     }     catch(myException& me)     {       cout<<me.what();     }     system("pause");     return 0;   }   

结果如下：

  Unexpected exception caught!  

请按任意键继续. . .                   

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